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An automatic control valve consists of three main parts in which each part exist in several types and designs: Valve actuator – which moves the valve's modulating element, such as ball or butterfly. Valve positioner – which ensures the valve has reached the desired degree of opening. This overcomes the problems of friction and wear.
A linear actuator opens and closes valves that can be operated via linear force, the type sometimes called a "rising stem" valve. These types of valves include globe valves, rising stem ball valves, control valves and gate valves. [2] The two main types of linear actuators are diaphragm and piston.
The ram-air inlet is a small scoop, generally located on the wing-to-body fairing. Nearly all jetliners use a modulating door on the ram-air inlet to control the amount of cooling airflow through the primary and secondary ram air heat exchangers. To increase ram-air recovery, nearly all jetliners use modulating vanes on the ram-air exhaust.
Proportional control overcomes this by modulating the output to the controlling device, such as a control valve at a level which avoids instability, but applies correction as fast as practicable by applying the optimum quantity of proportional gain.
From about 1932 onwards, the use of wideband pneumatic controllers increased rapidly in a variety of control applications. Air pressure was used for generating the controller output, and also for powering process modulating devices such as diaphragm-operated control valves.
Technically POPRV is the most generic term, but PORV is often used generically (as in this article) even though it should refer to valves in liquid service. In conventional PRVs, the valve is normally held closed by a spring or similar mechanism that presses a disk or piston on a seat, which is forced open if the pressure is greater than the ...
Pressure independent control valves can be used with any control system. The actuator options give a choice of thermal, 3-point control, or modulating control. This will work with building management systems and individual room controls, in the same way as traditional control valves. The actuators can also be used to set the valve by limiting flow.
A level control valve or altitude control valve is a type of valve that automatically responds to changes in the height of a liquid in some storage system. A common example is the set of ballcocks in a flush toilet, where each stage of the flush cycle is actuated by the emptying or filling of the tank.